The goals of this project are to develop a system of suppressor-sensitive genetics for animal viruses. We will characterize the chain-termination thymidine kinase mutants of herpes simplex virus by peptide mapping and in vitro protein synthesis. These mutants will be used to isolate host cells which carry suppressor genes. Such cell lines will be studied by in vivo and in vitro protein synthesis to determine the nature of the genetic suppression. These host cells will be used to isolate suppressor-sensitive mutants of animal viruses (HSV and SV-40) for genetic analysis.